Polyphase sequences for wireless communications

ABSTRACT

Polyphase sequence generation is provided for sequences having good aperiodic correlation properties. The sequences can allow lengths not attainable by other types of sequences (such as Frank sequences) and can yield increase merit factors and more desirable peak-to-side-peak ratios (and therefore decreased sidelobe energy) than other sequences (such as Chu sequences). Perfect root-of-unity sequences of lengths up to 32, achieving the minimum phase alphabets and the maximum merit factors and/or peak-to-side-peak ratios, are searched, and the results are tabulated. Comparing the merit factors and peak-to-side-peak ratios of the best search results to other sequences, a common construction pattern of the improved sequences of length 2m 2  are obtained. The improved sequences can be utilized in a variety of configurations, including spread spectrum communication, radar, channel estimation, system identification, and/or the like.

RELATED APPLICATION

This patent application is a continuation application of U.S. patentapplication Ser. No. 12/183,005, filed Jul. 30, 2008, and entitled“POLYPHASE SEQUENCES FOR WIRELESS COMMUNICATIONS,” the entirety of whichpatent application is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationssystems, and more particularly to polyphase sequences used to transmitsignals in wireless communications.

BACKGROUND

Due to the broadcast nature of wireless communications systems, such asspread spectrum communications, radar, mobile device communications,etc., communicating devices need to differentiate between and/orsynchronize with signals being transmitted by other devices in a givenproximity. In addition, where the transmitting device is also receivingits signal, it needs to differentiate that signal from other signals.This can be accomplished by applying polyphase sequences to transmitsignals, applying the sequences as communications preambles or headersfor timing synchronization and channel estimation, and/or the like. Somepolyphase sequences, more specifically constant amplitude zeroautocorrelation (CAZAC) sequences, have evolved including Franksequences, which are constrained to square numbered lengths, and Chusequences, which are constrained to prime numbered lengths, whenpairwise cross correlation properties need to be optimal.

Designed polyphase sequences can be application specific, for example.For radar, a utilized polyphase sequence exhibiting low sidelobe energycan be desired. Merit factors and/or peak-to-side-peak ratios can beutilized to measure total sidelobe energy and/or peak sidelobe energy.Chu and Frank sequences have tolerable merit factors andpeak-to-side-peak ratios, and thus are used in implementationscurrently; however, Frank sequences are severely limited in availablelengths, and Chu sequences require larger alphabet sizes to achievedesirable sidelobe energy. In addition, improved implementations seek toraise Frank sequence merit factors to more desirable levels, but do soat the cost of further increasing alphabet size. However, increasedalphabet sizes typically lead to increased system implementation cost.

SUMMARY

The following presents a simplified summary of the claimed subjectmatter in order to provide a basic understanding of some aspects of theclaimed subject matter. This summary is not an extensive overview of theclaimed subject matter. It is intended to neither identify key orcritical elements of the claimed subject matter nor delineate the scopeof the claimed subject matter. Its sole purpose is to present someconcepts of the claimed subject matter in a simplified form as a preludeto the more detailed description that is presented later.

Polyphase sequences are provided for utilization in wirelesscommunications systems (e.g., spectrum spread communications, radarapplications, system identification, channel estimation, etc.). Inparticular, polyphase sequences of length 2m², where m is an integer inthe set of natural numbers, are presented having improved merit factorsand peak-to-side-peak ratios than Chu sequences at sequence lengthsunavailable with Frank sequences. This can result in lowered sidelobeenergy. The sequences, in one example, can be perfect sequences withzero periodic autocorrelation functions for out-of-phase offsets asdescribed herein. Moreover, the sequences can have an alphabet sizesmaller than the Chu sequences (a square root smaller in some cases),which can decrease implementation costs required to use the sequences.According to an example, the sequences are constructed by performing anexhaustive search over perfect root of unity sequences (PRUS) of aspecified length, measuring the merit factors and peak-to-side-peakratios of sequences to determine those having optimal results, anddetermining a common construction among the sequences.

To the accomplishment of the foregoing and related ends, certainillustrative aspects of the claimed subject matter are described hereinin connection with the following description and the annexed drawings.These aspects are indicative, however, of but a few of the various waysin which the principles of the claimed subject matter can be employed.The claimed subject matter is intended to include all such aspects andtheir equivalents. Other advantages and novel features of the claimedsubject matter can become apparent from the following detaileddescription when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a high-level block diagram of an example system thatcan transmit signals associated with polyphase sequences.

FIG. 2 illustrates a block diagram of an example wireless transmitter inaccordance with various aspects.

FIG. 3 illustrates a block diagram of an example system for utilizingpolyphase sequences in wireless communications.

FIG. 4 illustrates an exemplary flow chart for applying polyphasesequences to one or more signals.

FIG. 5 illustrates an exemplary flow chart for searching andconstructing polyphase sequences with desirable merit factors and/orpeak-to-side-peak ratios.

FIG. 6 illustrates an exemplary graph related to merit factors andpeak-to-side-peak ratios of the optimal polyphase sequences describedherein.

FIG. 7 illustrates exemplary graphs of ambiguity factors for the optimalpolyphase sequences described herein and Chu sequences.

FIG. 8 illustrates an exemplary graph comparing merit factors of theoptimal polyphase sequences presented herein and Chu sequences.

FIG. 9 illustrates an exemplary graph comparing peak-to-side-peak ratiosof the optimal polyphase sequences described herein and Chu sequences.

FIG. 10 illustrates an exemplary graph comparing decibel representationsof merit factors and peak-to-side-peak ratios of the optimal polyphasesequences presented herein and Chu sequences.

FIG. 11 illustrates an exemplary graph comparing alphabet sizes of theoptimal polyphase sequences presented herein and Chu sequences.

FIG. 12 illustrates a block diagram of an example operating environmentin which various aspects described herein can function.

FIG. 13 illustrates an example wireless communication network in whichvarious aspects described herein can be utilized.

FIG. 14 illustrates an overview of a wireless network environmentsuitable for service by various aspects described herein.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order tofacilitate describing the claimed subject matter.

As used in this application, the terms “component,” “system,” and thelike are intended to refer to a computer-related entity, eitherhardware, a combination of hardware and software, software, or softwarein execution. For example, a component may be, but is not limited tobeing, a process running on a processor, a processor, an object, anexecutable, a thread of execution, a program, and/or a computer. By wayof illustration, both an application running on a server and the servercan be a component. One or more components may reside within a processand/or thread of execution and a component may be localized on onecomputer and/or distributed between two or more computers. Also, themethods and apparatus of the claimed subject matter, or certain aspectsor portions thereof, may take the form of program code (i.e.,instructions) embodied in tangible media, such as floppy diskettes,CD-ROMs, hard drives, or any other machine-readable storage medium,wherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing theclaimed subject matter. The components may communicate via local and/orremote processes such as in accordance with a signal having one or moredata packets (e.g., data from one component interacting with anothercomponent in a local system, distributed system, and/or across a networksuch as the Internet with other systems via the signal).

Additionally, while the present disclosure generally relates to singlecarrier communications systems, such as radar, and multiple carriercommunications systems, such as Orthogonal Frequency DivisionMultiplexing (OFDM), those skilled in the art will recognize that theclaimed subject matter can be used and applied in any wired or wirelesscommunication system that utilizes polyphase sequences to transmit andinterpret data between devices. It is to be appreciated that the systemsand/or methods described herein can be employed in any suitable wirelesscommunication system and that all such systems are intended to fallwithin the scope of the hereto appended claims.

Moreover, complex polyphase sequences refer to numeric sequences withlength L and denoted {s(n)} where 0≦n≦L−1. For n≧L, s(n)=s(n mod L).Periodic cross-correlation function of two sequences {s₁(n)} and{s₂(n)}, θ_(x)(τ), 0≦τ≦L−1 can be defined as

${\theta_{x}(\tau)} = {\sum\limits_{n = 0}^{L - 1}\; {{s_{1}(n)}{s_{2}^{*}\left( {n + \tau} \right)}}}$

where ()* denotes the complex conjugate operator. The periodicautocorrelation of a sequence {s(n)} can be the correlation itself givenas

${\theta_{ss}(\tau)} = {\sum\limits_{n = 0}^{L - 1}\; {{s(n)}{{s^{*}\left( {n + \tau} \right)}.}}}$

In addition, perfectness, or a perfect sequence is intended to refer toa sequence whose out-of-phase periodic autocorrelation is zero (e.g.,θ_(ss)(τ)=0, ∀τ≠0). It is to be appreciated that an aperiodicautocorrelation function, φ_(ss)(τ), can be computed similarly exceptthat such a function need not be computed over the entire sequence oflength L−1, but rather to L −1−τ. A root of unity sequence can refer toa sequence whose elements s(n), mε[0,N) are all complex roots of unity.In this regard, s(n) is in the form of exp(i2πx), where x is a rationalnumber. For example, exp(i2π/6) is root of unity while exp(i2π/√{squareroot over (2)}) is not. In addition, alphabet size can be defined as theminimum integer p such that s^(p)(n)=1, ∀nε[0,L). Thus, the alphabetsize exists for root of unity sequences; for example, the alphabet sizeof a binary sequence is 2. Also, {exp(i2π/6), exp(i2π/3), exp(i2π/4),exp(i2π/5)} has an alphabet size of 60. Further, a perfect root of unitysequence (PRUS) refers to a sequence that is perfect and root of unity,and constant amplitude zero autocorrelation (CAZAC) sequence refers to aperfect sequence whose amplitude is constant. Therefore, a PRUS is aCAZAC sequence, but a CAZAC sequence is not necessarily a PRUS.

Moreover, merit factors and peak-to-side-peak ratios can be computedfrom the aperiodic autocorrelation function φ_(ss)(τ) described above.Thus, a merit factor F for substantially any perfect root-of-unitysequence, defined as the main sidelobe to total sidelobe energy ratio,can be computed as

$F = {\frac{L^{2}}{2{\sum\limits_{\tau = 1}^{L - 1}\; {{\varphi_{ss}(\tau)}}^{2}}}.}$

Further, the peak-to-side-peak ratio R of a PRUS, another importantdesirable property, can be measured using the following equation

$R = {\frac{L}{\max_{1 \leq \tau \leq {L - 1}}{{\varphi_{ss}(\tau)}}}.}$

Additionally, Chu sequences are described herein and can refer tosequences of length L constructed by the following equation

${s_{Chu}(n)} = \left\{ \begin{matrix}{\exp\left( {\; \pi \frac{n^{2}M}{L}} \right)} & {{if}\mspace{14mu} L\mspace{14mu} {is}\mspace{11mu} {even}} \\{\exp \left( {{\pi}\frac{{n\left( {n + 1} \right)}M}{L}} \right)} & {{if}\mspace{14mu} L\mspace{14mu} {is}\mspace{14mu} {odd}}\end{matrix} \right.$

where M is an integer co-prime to L and can also be called thedecimation factor. Furthermore, Frank sequences are discussed and can beconstructed as follows

s _(Frank)(n)=exp(i2πpq/√{square root over (L)})

with p=└n/√{square root over (L)}┘ and q=n mod√{square root over (L)}

where └┘ is the floor operation. In this regard, for Chu sequences,length L can be substantially any natural number where Frank sequencesare limited to square numbers. Pairwise correlated sequence sets can beconstructed for the Frank and Chu sequences as well. For a sequence setwith set size K, there are K sequences in the set and the worst casepairwise cross correlation can be

$Y = {\max\limits_{1 \leq i \leq j \leq K}{\left\{ {\max\limits_{0 \leq \tau < L}{{\sum\limits_{n = 0}^{L - 1}\; {{s_{i}(n)}{s_{j}^{*}\left( {n + \tau} \right)}}}}} \right\}.}}$

The minimum achievable cross correlation for sequences of length L canbe √{square root over (L)}. Thus, an optimal set of decimated Franksequences of length L=m² can have a set size of m−1 for prime m. Inaddition, Chu sequences sets with prime length L and set size L−1 can beconstructed as

${s_{u}(n)} = {\exp \left\{ {\; 2\; \pi \; u\frac{n\left( {n + 1} \right)}{2L}} \right\}}$

where u is a sequence index that can be substantially any integerε{1,L). It is to be appreciated that the sequence length is furtherlimited to a prime number and the square of prime number for Chu andFrank sequence sets respectively.

As described previously, polyphase sequences can be utilized in timesynchronization for wireless communications systems, channel estimation,cell identification, and/or the like. For example, time synchronizationcan be achieved by correlating a received sequence {r(n)} with thereference sequence {s(n)}. As the sequence {s(n)} is perfect withoutnoise, the offset τ that results in a peak is the starting boundary of asymbol. {r(n)} can be obtained from the received stream with a slidingwindow of size L.

$b = {\arg \left\{ {\max\limits_{0 \leq \tau < L}{{\sum\limits_{n = 0}^{L - 1}\; {{r(n)}{s^{*}\left( {n + \tau} \right)}}}}} \right\}}$

In this operation, for example, the perfectness property, as describedpreviously, is used. In an OFDM system, channel coefficients forestimation can be obtained, for example, by dividing the receivedsequence elements by the reference sequence elements in the frequencydomain, for example.

h(n)=r(n)/s(n), n=0,1, . . . , L−1

In addition, for cell identification where each cell can be assigned asequence, cells can be identified by determining a sequence index uassigned to the cell. This can be determined by correlation as shown inthe following equation.

$u = {\arg \left\{ {\max\limits_{1 \leq i \leq K}\left\{ {\max\limits_{0 \leq \tau < L}{{\sum\limits_{n = 0}^{L - 1}\; {{r(n)}{s_{i}^{*}\left( {n + \tau} \right)}}}}} \right\}} \right\}}$

where {r(n)} is the received sequence. As shown, the correlation can becomputed between the received sequence and each sequence in the set;also, the sequence index that results in maximum correlation can bedetermined in this regard. In this example, this can be by utilizing thelow pairwise cross correlation property of the sequence set.

Unified construction of PRUS can be presented as well. A PRUS of lengthL=sm² can be constructed as

${s(n)} = {\exp \left( {\; 2\pi \frac{{m\; {c(s)}{\alpha (l)}k^{2}} + {{\beta (l)}k} + {f_{l}(0)}}{sm}} \right)}$where ${{c(s)} = \begin{Bmatrix}{1/2} & {{if}\mspace{14mu} s\mspace{14mu} {is}\mspace{14mu} {even}} \\1 & {otherwise}\end{Bmatrix}},$

nεZ_(sm) ² , l=n mod m, k=└n/m┘, α(l)εZ_(s) is a function withgcd(α(l),s)=1, ∀lεZ_(m), β(l)εZ_(sm) is a function such that β(l) (modm) is a permutation of the elements of Z_(m), and f_(l)(0), ∀lεZ_(m) arerational numbers. In this example, Z_(m) denotes non-negative integersless than m, and i is the imaginary unit. Additionally, to this end, aminimum alphabet size A_(mm) for the foregoing can be computed as

$A_{\min} = {\begin{Bmatrix}{2\; {sm}} & {{if}\mspace{14mu} s\mspace{14mu} {is}\mspace{14mu} {even}\mspace{14mu} {and}\mspace{14mu} m\mspace{14mu} {is}\mspace{14mu} {odd}} \\{sm} & {otherwise}\end{Bmatrix}.}$

Referring to FIG. 1, a high-level block diagram of a wirelesscommunication system 100 in accordance with various aspects presentedherein is illustrated. In one example, the system 100 includes apolyphase sequence component 102 that can generate and apply one or morepolyphase sequences to utilize in communicating with one or more devicesand a transmitter component 104 that transmits polyphase sequenceapplied data. In one example, the polyphase sequence component 102 canreceive data to transmit. The polyphase sequence component 102 can applyor associate a polyphase sequence with the data, and utilize thetransmitter component 104 to transmit the data to one or more devices.The polyphase sequence can be determined by a receiver and used todifferentiate the transmission from that of other devices, estimatecommunication channels, synchronize communications between devices,and/or the like. It is to be appreciated that the components shown canbe implemented in substantially any single or multiple carriercommunication system, including but not limited to spread spectrumsystems, radar, multiple access wireless systems (e.g., OFDMconfigurations), and/or the like.

According to an example, the polyphase sequences utilized by thepolyphase sequence component 102 can have good aperiodic correlationproperties, such as good merit factors and desirable peak-to-side-peakratios. The sequence can be perfect with zero periodic autocorrelationfunctions for out-of-phase offsets. These properties can relate to totalsidelobe energy and peak sidelobe energy for single carriercommunications, such as radar. The polyphase sequences can be applied tocommunications by the polyphase sequence component 102 and transmittedby the transmitter component 104 with low sidelobe energy levels forradar, system identification, etc. According to one example, thepolyphase sequences generated for use in the polyphase sequencecomponent 102 can be of length 2m², mεN, the set of natural numbers, andcan perform better than Chu sequences while providing length sizesunattainable by Frank sequences. Moreover, the sequences utilized by thepolyphase sequence component 102 can have decreased alphabet sizes whencompared to the Chu sequences. This can result in easier implementationof systems utilizing the polyphase sequence component 102. In oneexample, correlating sequences using digit-by-digit type methods, suchas coordinate rotation digital computer (CORDIC), can result incomplexity that can be linearly proportional to a phase alphabet size.Thus, reducing the alphabet size results in lower complexity, andtherefore decreased system implementation cost.

Turning to FIG. 2, a block diagram of an example wireless transmitter200 in accordance with various aspects is illustrated. The wirelesstransmitter 200 can be employed in a variety of environments includingradar, system identification, spread spectrum communications, etc. Inone example, the wireless transmitter 200 can include a polyphasesequence component 202 that can generate one or more polyphase sequencesexhibiting desirable properties, as described, such as good meritfactors and peak-to-side-peak ratios for decreased sidelobe energy. Inaddition, the wireless transmitter 200 can include a signal generationcomponent 204 that can create signals for transmission where the signalsare constructed from a sequence generated by the polyphase sequencecomponent 202. In one example, the signal can be created from parametersspecified by the signal generation component 204 and/or anothercomponent of the wireless transmitter 200. Moreover, a transmittercomponent 206 can be provided to transmit the signals to one or moredevices or objects (e.g., for receipt thereof by the device or torebound from the device/object in a radar system).

According to an example, the polyphase sequence component 202 cangenerate a polyphase sequence exhibiting the aforementioned desirableaperiodic correlation properties. For example, the polyphase sequencescan be of lengths L=sm² where s and m are non-negative integers andconstructed as PRUS shown above where

α(l) = 1;${{\beta (l)} = {\left\lfloor \frac{{3m} - 1}{2} \right\rfloor - l}};$f_(l)(0) = 0;

and lεZ_(m). In addition, in this example, s can be 2. Thus, thepolyphase sequence component 202 can construct sequences according tothe following equation,

${s(n)} = {\exp\left( {\; 2\pi \frac{{{m/2}k^{2}} + {{\beta (l)}k}}{2m}} \right)}$with k = ⌊n/m⌋ and${\beta (l)} = {\left\lfloor \frac{{3m} - 1}{2} \right\rfloor - \left( {n\mspace{14mu} {mod}\mspace{14mu} m} \right)}$

which produces sequences having improved merit factors andpeak-to-side-peak ratios over Chu sequences at lengths unavailable usingFrank sequences as shown infra. In addition, the alphabet size requiredfor the above sequences are a fraction of that required for Chusequences to achieve substantially similar performance. In addition,where L is an even number of the value 2m², the alphabet sizeA_(Chu)=2L. However, the sequences proposed, where of length L, resultin an alphabet size of

${A = \begin{Bmatrix}\sqrt{8L} & {{if}\mspace{14mu} \sqrt{L/2}\mspace{14mu} {is}\mspace{14mu} {odd}} \\\sqrt{2L} & {{if}\mspace{14mu} \sqrt{L/2}\mspace{14mu} {is}\mspace{14mu} {even}}\end{Bmatrix}},$

a reduction factor of √{square root over (2L)} from that of Chusequences. This can lead to easier or lower cost implementation of apolyphase sequence component 202 for generating the sequences as shownabove. In addition, such a low alphabet size requirement allows forextending the utilized alphabet size to further improve merit factors.In one example, the signal generation component 204 and/or anothercomponent of the wireless transmitter 200 can specify a desired length Lfor the sequence, from which m and/or an alphabet size A can becomputed. Additionally or alternatively, the alphabet size can bespecified from which the requisite length can be calculated using theabove formulas.

The signal generation component 204 can receive a polyphase sequencefrom the polyphase sequence component 202 to utilize in transmittingdata to one or more devices or broadcasting such for reflection from oneor more objects. The polyphase sequence can be specific for the wirelesstransmitter 200 in a communications environment, specific to a receiverof the signal (or object reflecting the signal), specific to a messagetransmitted or information desired in return, and/or the like. Thus, thepolyphase sequence can be differentiated for identification purposes ofthe transmitter and/or receiver (or reflector in a radarimplementation). In addition, the polyphase sequence can be applied todata by the signal generation component 204. This can be a directapplication affecting structure of the data, such as a scrambling,modulation, binary operation, choosing signals relating to data values,etc. with the sequence, or an indirect application, such as adding thesequence to a preamble (e.g., OFDM preamble) or other portion of thecommunication comprising parameters regarding the communication. Upongenerating the signal, the transmitter component 206 can transmit thesignal to one or more devices, or to be reflected from one or moredevices as described.

Turning to FIG. 3, a block diagram of an example system 300 that canconstruct polyphase sequences for use in wireless communications isshown. In particular, a polyphase sequence component 302 is providedthat can generate polyphase sequences as described. The sequences can beutilized with a wireless device 304 in a wireless network, in oneexample. The polyphase sequence component 302 comprises a sequencesearch component 306 that can search a number of sequences to determinethose having desirable properties and/or infer variables that can beutilized to construct such sequences for various lengths and alphabetsizes. The polyphase sequence component 302 can also comprise a sequenceconstruction component 308 that can create sequences based at least inpart on results from the sequence search component 306 and a sequenceapplication component 312 that can apply one or more constructedsequences to desired data. The sequence applied data can be utilized incommunicating with a wireless device 304, in one example.

According to an example, the sequence search component 306 can performan exhaustive search for PRUS, defined above, having a maximum meritfactor F for small sequence length L. In one example, the sequencesearch component 306 can perform some invariant operations to changesequence without significantly altering the absolute value of itsautocorrelation function (ACF), which can significantly reduce thesearch space. For example, the sequence search component 306 can apply alinear phase shift to substantially every element of a sequence—thisdoes not alter the absolute value of the ACF. Moreover, the sequencesearch component 306 can perform cyclic shifting as this does notsubstantially alter the ACF. In addition, the sequence search component306 can evaluate a complex conjugate of a sequence as it has asubstantially identical value for ACF. Additionally, the sequence searchcomponent 306 can consider sequences that are reflections of evaluatedsequences as the reflections have substantially the same merit factors.

Moreover, for any perfect sequence, it can be shownφ_(ss)(τ)=−φ*_(ss)(N−τ) and φ_(ss)(τ)=0 if τ(mod sm)=0.

$\begin{matrix}{{\theta_{ss}(\tau)} = {\sum\limits_{n = 0}^{L - 1}\; {{s(n)}{s^{*}\left( {n + \tau} \right)}}}} \\{= {{\varphi_{ss}(\tau)} + {\sum\limits_{n = {L - \tau}}^{L - 1}\; {{s(n)}{s^{*}\left( {n + \tau - L} \right)}}}}} \\{= {{\varphi_{ss}(\tau)} + {\sum\limits_{n = 0}^{\tau - 1}\; {{s\left( {n + L - \tau} \right)}{s^{*}(n)}}}}} \\{= {{\varphi_{ss}(\tau)} + \left\lbrack {\sum\limits_{n = 0}^{L - {({L - \tau})} - 1}\; {{s^{*}\left( {n + L - \tau} \right)}{s(n)}}} \right\rbrack^{*}}} \\{= {{\varphi_{ss}(\tau)} + {\varphi_{ss}^{*}\left( {L - \tau} \right)}}} \\{= 0}\end{matrix}$

Considering these additional properties, the sequence search component306 can reduce the computational requirement for the search. Thesequence search component 306 can initially construct PRUS as describedsupra and compute the merit factor to determine if it meets a threshold.It is to be appreciated that the peak-to-side-peak can be computed andcompared to a threshold as well. Where m=1, the sequence searchcomponent 306 can determine that Chu sequences are optimal. For squarelength sequences (e.g., L=4, 9, 16, . . . ), Frank sequences can beoptimal in some cases. However, for example, where L=sm², s=2, and m>1,the sequences described herein are determined to have optimal meritfactors and/or peak-to-side-peak ratios by the sequence search component306. After applying invariant transforms to these other superiorsequences, the sequence search component 306 can determine a consistentconstruction pattern for the sequences, as shown above.

For example, as described above, where s=2, the sequence searchcomponent 306 can determine PRUS where α(l)=1;

${{\beta (l)} = {\left\lfloor \frac{{3m} - 1}{2} \right\rfloor - l}};$

f_(l)(0)=0; and lεZ_(m) have more desirable merit factors and/orpeak-to-side-peak ratios than Chu, Frank, or substantially any knownsequences. In addition, as described, the sequences can require smalleralphabet sizes than respective Chu and Frank sequences, which can resultin streamlined implementation of devices utilizing the polyphasesequence component 302 as shown above. Moreover, the sequenceconstruction component 308 can utilize the variables or parametersdetermined by the sequence search component 306 to create sequences forutilization in a communication environment. In one example, the sequenceconstruction component 308 can determine and/or receive desired lengthsor alphabet sizes for the sequences and construct the sequencesaccording to these parameters. It is to be appreciated that theseparameters can be utilized by the sequence search component 306 in thesearch as well. Once constructed, the sequence application component 310can associate the sequences with wireless communications; in oneexample, the communications can relate to wireless device 304 and thesequences can be applied to data related thereto, whether modulated withthe data, placed in a header, and/or the like as previously described.

Referring now to FIGS. 4-5, methodologies that can be implemented inaccordance with various aspects described herein are illustrated. While,for purposes of simplicity of explanation, the methodologies are shownand described as a series of blocks, it is to be understood andappreciated that the claimed subject matter is not limited by the orderof the blocks, as some blocks may, in accordance with the claimedsubject matter, occur in different orders and/or concurrently with otherblocks from that shown and described herein. Moreover, not allillustrated blocks may be required to implement the methodologies inaccordance with the claimed subject matter.

Furthermore, the claimed subject matter may be described in the generalcontext of computer-executable instructions, such as program modules,executed by one or more components. Generally, program modules includeroutines, programs, objects, data structures, etc., that performparticular tasks or implement particular abstract data types. Typicallythe functionality of the program modules may be combined or distributedas desired in various embodiments. Furthermore, as will be appreciatedvarious portions of the disclosed systems above and methods below mayinclude or consist of artificial intelligence or knowledge or rule basedcomponents, sub-components, processes, means, methodologies, ormechanisms (e.g., support vector machines, neural networks, expertsystems, Bayesian belief networks, fuzzy logic, data fusion engines,classifiers . . . ). Such components, inter alia, can automate certainmechanisms or processes performed thereby to make portions of thesystems and methods more adaptive as well as efficient and intelligent.

Referring to FIG. 4, a methodology 400 that facilitates applyingpolyphase sequences having good merit factors and peak-to-side-peakratios to one or more signals is displayed. At 402, a desired polyphasesequence length for signal transmission is received. This can be from atransmitting device, such as a radar, wireless radio, spread spectrumdevice, etc., desiring to utilize a polyphase sequence in transmittingdata. The polyphase sequence can allow for system identification,channel estimation, and/or the like, as described, and/or provide signaltransmission with low sidelobe energy. At 404, a polyphase sequence withgood merit factors and/or peak-to-side-peak ratios can be determined asdescribed above.

For example, the sequence can be determined according to one or moreequations described above. In addition, the sequence can have a loweralphabet size than other sequences (such as Frank and/or Chu sequences).As shown, this can be beneficial in reducing implementation costs, forexample where CORDIC or other sequence correlation methods that increasein complexity as the required alphabet size grows are utilized. At 406,the polyphase sequence can be applied to data to generate a signal. Asdescribed, this can include modulating the data with the sequence,choosing sequences representative of different values, applying thesequence in a communication preamble or header, and/or the like. At 408,the signal can be transmitted to one or more devices. As mentioned, thedevices can receive the signal or rebound the signal (such as in a radarconfiguration). The signal can have low sidelobe energy related to themerit factor and/or peak-to-side-peak ratio.

Turning now to FIG. 5, a methodology 500 that facilitates searching forone or more sequences with good merit factors and/or peak-to-side-peakratios is shown. At 502, PRUS having certain lengths can be searched. Itis to be appreciated that as the length increases, the number of PRUSexhaustively searched can increase exponentially. However, utilizing theprinciples above can lessen the search burden (e.g., applying a linearphase shift, cyclic shifting, evaluating complex conjugates, etc.). At504, merit factors and/or peak-to-side-peak ratios for the PRUS can beevaluated. In the search, the PRUS having optimal merit factors and/orpeak-to-side-peal ratios can be noted. During or following the search,at 506, a common construction for PRUS having merit factors and/orpeak-to-side-peak ratios within a threshold can be determined Forexample, as described, using the PRUS formula to search, this caninclude PRUS where α(l)=1;

${{\beta (l)} = {\left\lfloor \frac{{3m} - 1}{2} \right\rfloor - l}};$

f_(l)(0)=0; and lεZ_(m). Thus, at 508, polyphase sequences can beconstructed according to this common construction and subsequentlyutilized in wireless communications.

Referring now to FIG. 6, illustrated is an example graph 600representing measured merit factors and peak-to-side-peak ratios of thedescribed sequences resulting from an exhaustive search over thesequences as discussed supra. The merit factors represented by line 602relate to those calculated as shown above for given sequence lengths.The peak-to-side-peak ratios, represented by line 604, are recorded aswell for each sequence length. For the sequences presented herein, thegraph 600 shows that merit factors and peak-to-side-peak ratiosgenerally increase as the sequence length increases; moreover, squaresequence lengths (e.g., sequence lengths whose square roots result in apositive integer) generally produce more desirable merit factors andpeak-to-side-peak ratios than adjacent lengths. Below is a correspondingtable of search results where sequences obtained by invarianttransforms, which are considered duplicate as described, are representedonly by one sequence (the sequence with minimum f_(l)(0), but where thef_(l)(0) for each are equal, the sequence with minimum β(l)).

Peak N A_(min) s Merit F Sidelobe α β f_(l)(0) 3 3 3 2.250 1.000 [1] [0][0] 4 2 1 4.000 1.000 [0 0] [0 1] [0 0] 5 5 5 4.523 1.000 [2] [0] [0] 612 6 3.600 1.000 [1] [0] [0] 7 7 7 3.830 1.247 [3] [0] [0] 8 4 2 4.0001.414 [1 1] [0 1] [0 0] 9 3 1 6.750 1.000 [0 0 0] [0 1 2] [0 0 0] 9 3 16.750 1.000 [0 0 0] [1 0 2] [0 0 1] 10 20 10 4.749 1.618 [1] [0] [0] 1111 11 4.951 1.683 [5] [0] [0] 12 6 3 5.143 2.000 [1 1] [3 0] [0 0] 12 63 5.143 1.732 [2 2] [2 3] [0 0] 12 6 3 5.143 1.732 [2 1] [1 4] [0 0] 1313 13 6.179 1.771 [6] [0] [0] 14 28 14 5.683 1.802 [1] [0] [0] 15 15 155.864 1.827 [7] [0] [0] 16 4 1 8.000 1.414 [0 0 0 0] [0 1 2 3] [0 0 0 0]16 4 1 8.000 2.000 [0 0 0 0] [1 0 3 2] [0 0 0 1] 17 17 17 6.915 1.891[8] [0] [0] 18 12 2 7.610 2.000 [1 1 1] [5 0 1] [0 0 0] 19 19 19 6.6532.094 [9] [0] [0] 20 10 5 6.970 2.149 [3 3] [4 5] [0 0] 21 21 21 7.5862.247 [10] [0] [0] 22 44 22 7.205 2.310 [1] [0] [0] 23 23 23 7.357 2.365[11] [0] [0] 24 12 6 7.629 2.394 [1 1] [0 1] [0 0] 25 5 1 12.362 1.940[0 0 0 0 0] [1 0 3 4 2] [0 0 0 0 1] 26 52 26 7.858 2.497 [1] [0] [0] 279 3 7.527 2.532 [2 2 2] [3 4 5] [0 0 0] 28 14 7 8.270 2.548 [4 4] [6 7][0 0] 29 29 29 8.782 2.592 [14] [0] [0] 30 60 30 8.462 2.618 [1] [0] [0]31 31 31 8.595 2.642 [15] [0] [0] 32 8 2 9.013 2.613 [1 1 1 1] [1 0 7 6][0 1 2 3]From the table, a construction pattern for sequences of length 2m² isnot obvious. However, after applying invariant transforms, as describedabove, the following consistent construction pattern can be obtained.

$\quad\left\{ \begin{matrix}{{\alpha = \left\lbrack {1\mspace{20mu} 1} \right\rbrack},{\beta = \left\lbrack {2\mspace{20mu} 1} \right\rbrack},{{{f_{l}(0)} = \left\lbrack {0\mspace{20mu} 0} \right\rbrack};}} & {{m = 2},{F = 4.000}} \\{{\alpha = \left\lbrack {1\mspace{20mu} 1\mspace{20mu} 1} \right\rbrack},{\beta = \left\lbrack {4\mspace{14mu} 3\mspace{14mu} 2} \right\rbrack},{{{f_{l}(0)} = \left\lbrack {0\mspace{20mu} 0\mspace{20mu} 0} \right\rbrack};}} & {{m = 3},{F = 7.610}} \\{{\alpha = \left\lbrack {1\mspace{20mu} 1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack},{\beta = \left\lbrack {5\mspace{20mu} 4\mspace{20mu} 3\mspace{20mu} 2} \right\rbrack},{{{f_{l}(0)} = \left\lbrack {0\mspace{20mu} 0\mspace{20mu} 0\mspace{20mu} 0} \right\rbrack};}} & {{m = 4},{F = 9.013}}\end{matrix} \right.$

Moreover, the above sequences in the search results, with s=3 and m=2,3, 4, not only have optimal merit factors F, but also result in thesmallest peak sidelobe (which can be related to the largestpeak-to-side-peak ratio). From these results, it can be determined thatPRUS where α(l)=1;

${{\beta (l)} = {\left\lfloor \frac{{3m} - 1}{2} \right\rfloor - l}};$

f_(l)(0)=0; and lεZ_(m) provide optimal results for sequences of lengthL=2m².

Turning now to FIGS. 7-11, various graphs are depicted comparing searchresults relating to the optimal sequences described herein to Chusequences. As will be appreciated when referring to the graphs, thesequences described herein produce more optimal results than Chusequences with respect to peak-to-side-peak ratios and merit factors ata fraction of the required alphabet size. Referring to FIG. 7, examplegraphs 700 and 702 are shown representing ambiguity functions for thesequences described herein and Chu sequences, respectively, for lengthL=32. The ambiguity function relates to time response of a filtermatched to a given finite energy signal where the signal is receivedwith a delay and a Doppler shift. As represented by the graphs, theambiguity functions for signals utilizing the sequences described hereinwhen compared to corresponding Chu sequences are quite similar. Thus,there is substantially no added distortion when utilizing the sequencespresented herein over the Chu sequences.

Now referring to FIGS. 8-9, example graphs 800 and 900 respectivelyshowing merit factors and peak-to-side-peak ratios of the sequencespresented herein (referred to as “new sequences”) as compared to thoseof conventional Chu sequences over square root of sequence length L aredisplayed. The circles 802 and 902 relate to merit factors andpeak-to-side-peak ratios, respectively, for the new sequences measuredin simulation, and the lines 804 and 904 respectively relate to newsequence merit factors and peak-to-side-peak ratios as measured byinterpolation for length 2m². Similarly, the asterisks 806 and 906respectively represent merit factors and peak-to-side-peak ratios ofconventional Chu sequences measured in simulation over the square rootof sequence length while the lines 808 and 908 represent the meritfactors and peak-to-side-peak ratios, respectively, of Chu sequencesmeasured through interpolation. It is evident, from the graphs 800 and900, that the merit factors F and peak-to-side-peak ratios R of thesequences increase substantially linearly with √{square root over (L)}.

In this regard, the merit factors and peak-to-side-peak ratios can beexpressed as first order polynomials of √{square root over (L)}.

F=a _(F) √{square root over (L)}+b _(F)

R=a _(R) √{square root over (L)}+b _(R)

Values for a_(F),b_(F),a_(R), and b_(R) can be obtained such that thefirst order polynomials above can fit the available points bysimulation, in the least square sense. The computed values can be

$\left( {a_{F},b_{F}} \right) = \left\{ {{\begin{matrix}\left( {1.5674,0.1185} \right) & {{Chu}\mspace{14mu} {sequence}} \\\left( {1.7520,{- 0.3396}} \right) & {{New}\mspace{14mu} {sequence}}\end{matrix}\left( {a_{R},b_{R}} \right)} = \left\{ \begin{matrix}\left( {2.0822,{- 0.0093}} \right) & {{Chu}\mspace{14mu} {sequence}} \\\left( {2.2298,{- 0.3217}} \right) & {{New}\mspace{14mu} {sequence}}\end{matrix} \right.} \right.$

The interpolation factors for the new sequences 804 and 904 and for theChu sequences 808 and 908 are plotted based on computation using theabove coefficients in the given first order polynomials. It is shownthat the sequences presented herein have coefficients approximately 0.2greater than Chu sequences, and thus have more optimal merit factors Fand peak-to-side-peak ratios R; the degree of optimality improves forthe sequences presented herein as the sequence length increases.

Referring now to FIG. 10, an example graph 1000 is illustratedcorresponding to comparing merit factors and peak-to-side-peak ratios ofsequences presented herein to conventional Chu sequences expressed indecibels as a function of sequence length L. In this example, the meritfactor can be represented by F_(dB)=10 log₁₀(F) and peak-to-side-peakratio by R_(dB)=20 log₁₀(R) for each sequence. Similarly to previousfigures, the circles 1002 on either the merit factor F curve 1010 or thepeak-to-side-peak ratio R curve 1012, represent present sequencesimulation results while the lines 1004 on either curve 1010 and/or 1012represent interpolation results. Moreover, the asterisks 1006 on eithercurve 1010 or curve 1012 represent simulation results of Chu sequenceswhile the lines 1008 represent corresponding interpolation results asdescribed above. Again, it is shown that the sequences presented hereinoutperform conventional Chu sequences in merit factor andpeak-to-side-peak ratio. In particular, while expressing merit factorsin decibel, F_(dB)≈5 log₁₀L+10 log₁₀a_(F) and R_(dB)≈10 log₁₀L+20log₁₀a_(R), the improvement in decibel can be independent of thesequence length L. For longer sequence lengths, as shown in the graph1000, improvements in decibel for merit factors F and peak-to-side-peakratios R for the sequences presented herein can reach and exceed 0.48 dBand 0.59 dB respectively.

Now turning to FIG. 11, an example graph 1100 of resulting alphabetsizes for the optimal sequences presented herein as compared to theconventional Chu sequences to achieve the performance factors above isillustrated. The alphabet size for increasing sequence length L for thesequences presented herein is shown at line 1102, while those forconventional Chu sequences are shown at line 1104. As describedpreviously and shown by the graph 1100, the alphabet size for thesequences presented herein are reduced by a factor of √{square root over(L/2)} or √{square root over (2L)} in some cases as compared to the Chusequences. Thus, as the sequence length increases, the difference inrequired alphabet sizes of the sequences presented herein and Chusequences is apparent. The reduced alphabet sizes, as mentionedpreviously, can result in easier implementation of the sequences in oneor more systems and can also provide room for increasing alphabet sizesto further improve merit factors.

Turning to FIG. 12, an exemplary non-limiting computing system oroperating environment in which various aspects described herein can beimplemented is illustrated. One of ordinary skill in the art canappreciate that handheld, portable and other computing devices andcomputing objects of all kinds are contemplated for use in connectionwith the claimed subject matter, e.g., anywhere that a communicationssystem may be desirably configured. Accordingly, the below generalpurpose remote computer described below is but one example of acomputing system in which the claimed subject matter can be implemented.

Although not required, the claimed subject matter can partly beimplemented via an operating system, for use by a developer of servicesfor a device or object, and/or included within application software thatoperates in connection with one or more components of the claimedsubject matter. Software may be described in the general context ofcomputer executable instructions, such as program modules, beingexecuted by one or more computers, such as client workstations, serversor other devices. Those skilled in the art will appreciate that theclaimed subject matter can also be practiced with other computer systemconfigurations and protocols.

FIG. 12 thus illustrates an example of a suitable computing systemenvironment 1200 in which the claimed subject matter can be implemented,although as made clear above, the computing system environment 1200 isonly one example of a suitable computing environment for a media deviceand is not intended to suggest any limitation as to the scope of use orfunctionality of the claimed subject matter. Further, the computingenvironment 1200 is not intended to suggest any dependency orrequirement relating to the claimed subject matter and any one orcombination of components illustrated in the example operatingenvironment 1200.

With reference to FIG. 12, an example of a remote device forimplementing various aspects described herein includes a general purposecomputing device in the form of a computer 1210. Components of computer1210 can include, but are not limited to, a processing unit 1220, asystem memory 1230, and a system bus 1221 that couples various systemcomponents including the system memory 1230 to the processing unit 1220.The system bus 1221 can be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures.

Computer 1210 can include a variety of computer readable media. Computerreadable media can be any available media that can be accessed bycomputer 1210. By way of example, and not limitation, computer readablemedia can comprise computer storage media and communication media.Computer storage media includes volatile and nonvolatile as well asremovable and non-removable media implemented in any method ortechnology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CDROM, digital versatile disks (DVD)or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canbe accessed by computer 1210. Communication media can embody computerreadable instructions, data structures, program modules or other data ina modulated data signal such as a carrier wave or other transportmechanism and can include any suitable information delivery media.

The system memory 1230 can include computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) and/orrandom access memory (RAM). A basic input/output system (BIOS),containing the basic routines that help to transfer information betweenelements within computer 1210, such as during start-up, can be stored inmemory 1230. Memory 1230 can also contain data and/or program modulesthat are immediately accessible to and/or presently being operated on byprocessing unit 1220. By way of non-limiting example, memory 1230 canalso include an operating system, application programs, other programmodules, and program data.

The computer 1210 can also include other removable/non-removable,volatile/nonvolatile computer storage media. For example, computer 1210can include a hard disk drive that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive thatreads from or writes to a removable, nonvolatile magnetic disk, and/oran optical disk drive that reads from or writes to a removable,nonvolatile optical disk, such as a CD-ROM or other optical media. Otherremovable/non-removable, volatile/nonvolatile computer storage mediathat can be used in the exemplary operating environment include, but arenot limited to, magnetic tape cassettes, flash memory cards, digitalversatile disks, digital video tape, solid state RAM, solid state ROMand the like. A hard disk drive can be connected to the system bus 1221through a non-removable memory interface such as an interface, and amagnetic disk drive or optical disk drive can be connected to the systembus 1221 by a removable memory interface, such as an interface.

A user can enter commands and information into the computer 1210 throughinput devices such as a keyboard or a pointing device such as a mouse,trackball, touch pad, and/or other pointing device. Other input devicescan include a microphone, joystick, game pad, satellite dish, scanner,or the like. These and/or other input devices can be connected to theprocessing unit 1220 through user input 1240 and associated interface(s)that are coupled to the system bus 1221, but can be connected by otherinterface and bus structures, such as a parallel port, game port or auniversal serial bus (USB). A graphics subsystem can also be connectedto the system bus 1221. In addition, a monitor or other type of displaydevice can be connected to the system bus 1221 via an interface, such asoutput interface 1250, which can in turn communicate with video memory.In addition to a monitor, computers can also include other peripheraloutput devices, such as speakers and/or a printer, which can also beconnected through output interface 1250.

The computer 1210 can operate in a networked or distributed environmentusing logical connections to one or more other remote computers, such asremote computer 1270, which can in turn have media capabilitiesdifferent from device 1210. The remote computer 1270 can be a personalcomputer, a server, a router, a network PC, a peer device or othercommon network node, and/or any other remote media consumption ortransmission device, and can include any or all of the elementsdescribed above relative to the computer 1210. The logical connectionsdepicted in FIG. 12 include a network 1271, such local area network(LAN) or a wide area network (WAN), but can also include othernetworks/buses. Such networking environments are commonplace in homes,offices, enterprise-wide computer networks, intranets and the Internet.

When used in a LAN networking environment, the computer 1210 isconnected to the LAN 1271 through a network interface or adapter 1260.When used in a WAN networking environment, the computer 1210 can includea communications component, such as a modem, or other means forestablishing communications over the WAN, such as the Internet. Acommunications component, such as a modem, which can be internal orexternal, can be connected to the system bus 1221 via the user inputinterface at input 1240 and/or other appropriate mechanism. In anetworked environment, program modules depicted relative to the computer1210, or portions thereof, can be stored in a remote memory storagedevice. It should be appreciated that the network connections shown anddescribed are exemplary and other means of establishing a communicationslink between the computers can be used.

Turning now to FIGS. 13-14, an overview of network environments in whichthe claimed subject matter can be implemented is illustrated. Theabove-described systems and methodologies can be applied to any wirelesscommunication network; however, the following description sets forthsome exemplary, non-limiting operating environments for said systems andmethodologies. The below-described operating environments should beconsidered non-exhaustive, and thus the below-described networkarchitectures are merely examples of network architectures into whichthe claimed subject matter can be incorporated. It is to be appreciatedthat the claimed subject matter can be incorporated into any nowexisting or future alternative communication network architectures aswell.

Referring first to FIG. 13, a wireless personal area network (WPAN)architecture 1300 based on the IEEE 802.15.3 high data rate WPANstandard is illustrated. Based on the IEEE 802.15.3 standard, the WPANarchitecture 1300 can include one or more piconets. As used herein, apiconet is an ad hoc network of independent data devices 1310-1328 thatcan engage in peer-to-peer communication. FIG. 13 illustrates one suchpiconet. In one example, the range of a piconet is confined to apersonal area of, for example, 10 to 50 meters, although a piconet canalternatively provide coverage for a larger or smaller coverage area.

In accordance with one aspect, a piconet can be established by a device1310 that is capable of becoming a piconet coordinator (PNC). The device1310 can establish the piconet by scanning a set of availablecommunication channels (e.g., communication channels corresponding totime frequency codes in an MB-OFDM communication environment) for achannel having a least amount of interference that is not in use byneighboring piconets. Once such a communication channel is found, thedevice 1310 can become a PNC and begin transmitting control messaging inthe form of beacons to allow other devices 1322-1328 to connect to thepiconet. As illustrated in architecture 1300, beacons transmitted by PNC1310 are shown by dotted lines.

Once a PNC 1310 establishes a piconet, one or more devices 1322-1328 canassociate with the PNC 1310 based on beacons transmitted by the PNC1310. In one example, beacons provided by a PNC 1310 can provide timinginformation, and a device 1322-1328 can perform one or more timingsynchronization techniques based on received beacons as described suprawhile associating with the piconet coordinated by the PNC 1310. Inaddition, beacons transmitted by the PNC 1310 can also containinformation relating to quality of service (QoS) parameters, time slotsfor transmission by devices 1322-1328 in the piconet, and/or othersuitable information. After a device 1322-1328 has successfullyassociated with the piconet, it can then communicate in the piconet bytransmitting data to the PNC 1310 and/or one or more other devices1322-1328 in the piconet. As illustrated in architecture 1300, datatransmissions are indicated by solid lines.

In accordance with one aspect, the PNC 1310 and devices 1322-1328 canadditionally communicate using ultra-wideband (UWB) communication. WhenUWB is used, the PNC 1310 and/or devices 1322-1328 can communicatebeacons and/or data using short-duration pulses that span a wide rangeof frequencies. In one example, transmissions made pursuant to UWB canoccupy a spectrum of greater than 20% of a center frequency utilized bythe network or a bandwidth of at least 500 MHz. Accordingly, UWBtransmissions can be conducted using a very low power level (e.g.,approximately 0.2 mW), which can allow UWB transmission to be conductedin common bands with other forms of communication without introducingsignificant interference levels. Because UWB operates at a low powerlevel, it should be appreciated that UWB is typically confined to asmall coverage area (e.g., approximately 10 to 100 meters), which cancorrespond to the coverage area of an associated piconet. However, bytransmitting in short radio bursts that span a large frequency range,devices utilizing UWB can transmit significantly large amounts of datawithout requiring a large amount of transmit power. Further, because ofthe large bandwidth range and low transmit power used in UWBtransmission, signals transmitted utilizing UWB can carry throughobstacles that can reflect signals at lower bandwidth or higher power.

Turning now to FIG. 14, various aspects of the global system for mobilecommunication (GSM) are illustrated. GSM is one of the most widelyutilized wireless access systems in today's fast growing communicationssystems. GSM provides circuit-switched data services to subscribers,such as mobile telephone or computer users. General Packet Radio Service(“GPRS”), which is an extension to GSM technology, introduces packetswitching to GSM networks. GPRS uses a packet-based wirelesscommunication technology to transfer high and low speed data andsignaling in an efficient manner. GPRS optimizes the use of network andradio resources, thus enabling the cost effective and efficient use ofGSM network resources for packet mode applications.

As one of ordinary skill in the art can appreciate, the exemplaryGSM/GPRS environment and services described herein can also be extendedto 3G services, such as Universal Mobile Telephone System (“UMTS”),Frequency Division Duplexing (“FDD”) and Time Division Duplexing(“TDD”), High Speed Packet Data Access (“HSPDA”), cdma2000 1x EvolutionData Optimized (“EVDO”), Code Division Multiple Access-2000 (“cdma20003x”), Time Division Synchronous Code Division Multiple Access(“TD-SCDMA”), Wideband Code Division Multiple Access (“WCDMA”), EnhancedData GSM Environment (“EDGE”), International MobileTelecommunications-2000 (“IMT-2000”), Digital Enhanced CordlessTelecommunications (“DECT”), etc., as well as to other network servicesthat shall become available in time. In this regard, the timingsynchronization techniques described herein may be applied independentlyof the method of data transport, and does not depend on any particularnetwork architecture or underlying protocols.

FIG. 14 depicts an overall block diagram of an exemplary packet-basedmobile cellular network environment, such as a GPRS network, in whichthe claimed subject matter can be practiced. Such an environment caninclude a plurality of Base Station Subsystems (BSS) 1400 (only one isshown), each of which can comprise a Base Station Controller (BSC) 1402serving one or more Base Transceiver Stations (BTS) such as BTS 1404.BTS 1404 can serve as an access point where mobile subscriber devices1450 become connected to the wireless network. In establishing aconnection between a mobile subscriber device 1450 and a BTS 1404, oneor more timing synchronization techniques as described supra can beutilized.

In one example, packet traffic originating from mobile subscriber 1450is transported over the air interface to a BTS 1404, and from the BTS1404 to the BSC 1402; the traffic can be transported using the polyphasesequences as described herein, in one example. Base station subsystems,such as BSS 1470, are a part of internal frame relay network 1410 thatcan include Service GPRS Support Nodes (“SGSN”) such as SGSN 1412 and1414. Each SGSN is in turn connected to an internal packet network 1420through which a SGSN 1412, 1414, etc., can route data packets to andfrom a plurality of gateway GPRS support nodes (GGSN) 1422, 1424, 1426,etc. As illustrated, SGSN 1414 and GGSNs 1422, 1424, and 1426 are partof internal packet network 1420. Gateway GPRS serving nodes 1422, 1424and 1426 can provide an interface to external Internet Protocol (“IP”)networks such as Public Land Mobile Network (“PLMN”) 1445, corporateintranets 1440, or Fixed-End System (“FES”) or the public Internet 1430.As illustrated, subscriber corporate network 1440 can be connected toGGSN 1422 via firewall 1432; and PLMN 1445 can be connected to GGSN 1424via boarder gateway router 1434. The Remote Authentication Dial-In UserService (“RADIUS”) server 1442 may also be used for callerauthentication when a user of a mobile subscriber device 1450 callscorporate network 1440.

Generally, there can be four different cell sizes in a GSMnetwork—macro, micro, pico, and umbrella cells. The coverage area ofeach cell is different in different environments. Macro cells can beregarded as cells where the base station antenna is installed in a mastor a building above average roof top level. Micro cells are cells whoseantenna height is under average roof top level; they are typically usedin urban areas. Pico cells are small cells having a diameter is a fewdozen meters; they are mainly used indoors. On the other hand, umbrellacells are used to cover shadowed regions of smaller cells and fill ingaps in coverage between those cells.

The claimed subject matter has been described herein by way of examples.For the avoidance of doubt, the subject matter disclosed herein is notlimited by such examples. In addition, any aspect or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs, nor is it meant to precludeequivalent exemplary structures and techniques known to those ofordinary skill in the art. Furthermore, to the extent that the terms“includes,” “has,” “contains,” and other similar words are used ineither the detailed description or the claims, for the avoidance ofdoubt, such terms are intended to be inclusive in a manner similar tothe term “comprising” as an open transition word without precluding anyadditional or other elements.

Additionally, the disclosed subject matter can be implemented as asystem, method, apparatus, or article of manufacture using standardprogramming and/or engineering techniques to produce software, firmware,hardware, or any combination thereof to control a computer or processorbased device to implement aspects detailed herein. The terms “article ofmanufacture,” “computer program product” or similar terms, where usedherein, are intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ),smart cards, and flash memory devices (e.g., card, stick). Additionally,it is known that a carrier wave can be employed to carrycomputer-readable electronic data such as those used in transmitting andreceiving electronic mail or in accessing a network such as the Internetor a local area network (LAN).

The aforementioned systems have been described with respect tointeraction between several components. It can be appreciated that suchsystems and components can include those components or specifiedsub-components, some of the specified components or sub-components,and/or additional components, according to various permutations andcombinations of the foregoing. Sub-components can also be implemented ascomponents communicatively coupled to other components rather thanincluded within parent components, e.g., according to a hierarchicalarrangement. Additionally, it should be noted that one or morecomponents can be combined into a single component providing aggregatefunctionality or divided into several separate sub-components, and anyone or more middle layers, such as a management layer, can be providedto communicatively couple to such sub-components in order to provideintegrated functionality. Any components described herein can alsointeract with one or more other components not specifically describedherein but generally known by those of skill in the art.

1. A non-transitory computer readable storage medium storingcomputer-executable instructions that, in response to execution, causean apparatus including a processor to perform operations, comprising:constructing polyphase perfect root of unity sequences (PRUS); andapplying at least one of the polyphase PRUS to data for transmission ofthe data.
 2. The non-transitory computer readable storage medium ofclaim 1, wherein the operations further comprise: determining meritfactors or peak-to-side-peak ratios of the polyphase PRUS.
 3. Thenon-transitory computer readable storage medium of claim 2, wherein thedetermining includes determining that the merit factors or thepeak-to-side-peak ratios of the polyphase PRUS outperform Chu sequences.4. The non-transitory computer readable storage medium of claim 1,wherein the operations further comprise: in response to the applying theat least one of the polyphase PRUS, initiating the transmission of thedata to at least one device.
 5. The non-transitory computer readablestorage medium of claim 1, wherein the operations further comprise:applying the at least one of the polyphase PRUS to a header of the datato differentiate the data from other data.
 6. The non-transitorycomputer readable storage medium of claim 1, wherein the constructingcomprises: accepting input parameters according to a defined length oran alphabet size for the polyphase PRUS.
 7. The non-transitory computerreadable storage medium of claim 1, wherein the polyphase PRUS are oflength L=sm² where s and m are positive integers.
 8. A system,comprising: means for searching a plurality of perfect root of unitysequences (PRUS); means for determining a PRUS from the plurality ofPRUS that determines a merit factor defined as a ratio of main sidelobeenergy to total sidelobe energy; and means for conveying data as afunction of the PRUS.
 9. The system of claim 8, wherein the means forsearching comprises: means for factoring at least one invariantoperation characteristic of the plurality of PRUS to reduce a number ofPRUS searched.
 10. The system of claim 8, wherein the means forsearching comprises: means for searching within a maximum length L=sm²where s and m are positive integers to bound a search space associatedwith the plurality of PRUS.
 11. A non-transitory computer readablestorage medium storing computer-executable instructions that, inresponse to execution, cause a system including a processor to performoperations, comprising: selecting a polyphase sequence from a set ofgenerated perfect root of unity sequences (PRUS); associating thepolyphase sequence with a signal; and causing the signal to betransmitted to at least one device.
 12. The non-transitory computerreadable storage medium of claim 11, wherein the operations furthercomprise: receiving the signal rebounded from the at least one device;and determining device information based at least in part on the signal.13. The non-transitory computer readable storage medium of claim 11,wherein the operations further comprise: modulating the signal with thepolyphase sequence; and associating the polyphase sequence with thesignal in response to the modulating.
 14. The non-transitory computerreadable storage medium of claim 11, wherein the associating comprises:selecting disparate sequences in the set of generated PRUS that map tovalues of the signal, wherein the disparate sequences are represented inthe signal.
 15. The non-transitory computer readable storage medium ofclaim 11, wherein the selecting comprises: searching for at least onePRUS that has a merit factor or a peak-to-side-peak ratio that satisfiesa condition; and selecting the at least one PRUS that satisfies thecondition.
 16. The non-transitory computer readable storage medium ofclaim 11, wherein the selecting comprises: selecting the polyphasesequence from the set of generated PRUS that are of length L=sm² where sand m are positive integers.
 17. The non-transitory computer readablestorage medium of claim 16, wherein the operations further comprise:accepting an input parameter defining L or m.
 18. A system, comprising:means for generating at least one polyphase sequence that has analphabet size lower than a Chu sequence; and means for transmitting theat least one polyphase sequence in a communication to a device.
 19. Thesystem of claim 18, wherein the means for transmitting comprises: meansfor using a sidelobe energy level determined to be lower than a Chusequence sidelobe energy level.
 20. The system of claim 18, furthercomprising: means for constructing a signal from the at least onepolyphase sequence and including the signal in the communication.